The invention relates generally to transportation vehicles or other devices powered by natural gas or other gaseous fuels stored at low-pressure. More particularly, the invention relates to such vehicles or devices having fuel storage apparatus employing sorbent materials (adsorbents and/or absorbents) and also to refueling apparatus for such vehicles.
Over the years, concerns have developed over the availability of conventional fuels (such as gasoline or diesel fuel) for internal combustion engine vehicles, the operating costs and fuel efficiencies of such vehicles, and the potentially adverse effects of vehicle emissions on the environment. Because of such concern, much emphasis has been placed on the development of alternatives to such conventional vehicle fuels. One area of such emphasis has been the development of vehicles fueled by natural gas or other methane-type gaseous fuels, either as the sole fuel or as one fuel in a dual-fuel system. As a result, vehicles using such fuels have been produced and are currently in use both domestically and abroad.
For example, it has been estimated that as many as 275,000 natural gas powered vehicles are currently in use in Italy alone. Indeed, natural gas has been used continuously in Italy as a motive fuel for at least 40 years. Natural gas has also been used as a motive fuel for vehicles in several other foreign countries, including France, New Zealand, Canada, Iran, Australia, Holland and the United Kingdom.
In the United States, it has been estimated that approximately 20,000 vehicles presently use natural gas. One of the initial efforts to employ natural gas as a vehicular fuel is represented by the Southern California Gas Company's conversion of approximately 1000 vehicles to a compressed natural gas (CNG) fueling system during 1969 and 1970. Today, dual-fuel conversion systems which enable an otherwise conventional vehicle to operate on either gasoline or natural gas are commercially available from several domestic and foreign manufacturers. While conversion kits to permit an otherwise conventional vehicle to operate solely on natural gas are not known to be generally commercially available, the Ford Motor Company has recently built a demonstration vehicle of this kind. This vehicle is based upon a Ford LN7 model 2-passenger automobile, and includes lightweight storage cylinders which are used to store a self-contained supply of natural gas.
A more detailed discussion of the development and use of natural gas as a motive fuel for vehicles may be found in the following publications, which are hereby incorporated by reference: "Compressed Natural Gas (CNG): A Vehicle Fuel for Utility Company Fleets--the Pros and Cons", American Gas Association, an operating section report issued February 1982; "Assessment of Methane-Related Fuels for Automotive Fleet Vehicles", prepared for the Department of Energy (DOE/CE/50179-1) by The Aerospace Corporation, February 1982.
In order to provide such gaseous fueled vehicles with a reasonable range of travel between refuelings, it has previously been necessary to store the on-board gaseous fuel at very high pressures, generally in the range of approximately, 2000 psig (13.7 MPa) to 3000 psig (20.7 MPa). Without such high-pressure on-board storage, the practical storage capacity of such vehicles was limited because of space and weight factors to the energy equivalent of approximately one to five gallons (3.7 to 19 liters,) of conventional gasoline. Thus, by compressing the gaseous fuel to such high pressures, the on-board storage capacities of such vehicles were increased to the point that reasonable travel ranges between refuelings were attainable.
One disadvantage of the compressed gaseous fuel systems discussed above is that they require complex, expensive and time-consuming refueling apparatus in order to compress the fuel to such high pressures. Such refueling apparatus has been found to effectively preclude refueling the vehicle from a user's residential natural gas supply system as being commercially impractical on an individual ownership basis.
Another disadvantage of high pressure on-board natural gas storage systems is that heavy walled containers must typically be used, thereby increasing the cost and weight of the system. Additionally, as the cylinders are discharged during the operation of the vehicle, significant condensation on associated piping can occur as a result of the magnitude of the decrease in the pressure inside the cylinder.
Another alternative to the above discussed fuel storage and vehicle range problems, has been to store the on-board fuel in a liquid state generally at or near atmospheric pressure in order to allow sufficient quantities of fuel to be carried on board the vehicles to provide reasonable travel ranges between refuelings. Such liquefied gas storage may also be disadvantageous if it involves complex and expensive cryogenic equipment, both on board the vehicle and in the refueling station, in order to establish and maintain the necessary low gas temperatures.
In non-vehicular gaseous fuel storage applications for stationary installations, it has been found that the use of high-surface-area adsorptive materials has provided for significantly increased storage capacities at relatively low pressures. Such adsorptive materials typically include zeolites, activated carbons and silica gels. For example, the Spangler U.S. Pat. No. 2,712,730, issued on July 12, 1955, discloses a method and apparatus for storing various types of (liquefied) hydrocarbon gases which utilizes an adsorbent in order to increase the storage capacity of the stationary system.
In vehicular applications, the use of high-surface-area materials to adsorb natural gas was suggested as a potential means for increasing the on-board gas storage capacity at least as early as August 1971, in a report entitled "Natural Gas Storage With Zeolites". This report by Ronald A. Munson and Robert a Clifton, Jr. was published by the U.S. Department Of The Interior, Bureau of Mines (technical progress report 38), and is hereby incorporated by reference. A preliminary analysis of this concept was also presented in Section 2.2.3 of the "Assessment of Methane-Related Fuels for Automotive Fleet Vehicles" report identified above. The calculations used in this analysis indicated that a natural gas storage system utilizing adsorption would weigh approximately twice as much as a conventional high-pressure natural gas storage system.
The extent to which research efforts have been directed to developing a vehicular adsorption fuel storage system are exemplified by the recent efforts of the Ford Motor Company. Two papers were presented at the Fourth International Conference on Alternative Energy Sources, Miami Beach, Fla., December 1981, namely "Adsorption of Methane on Active Carbons and Zeolites" by K. Otto, and "Low Pressure Methane Storage Systems For Vehicles--Preliminary Concept Evaluation" by J. Braslow et al, which are both hereby incorporated by reference. These papers discussed laboratory experiments directed to determining the effect of the heat of methane adsorption on carbon capacity and the limitations of methane storage by adsorption.
Significantly, in Ford's most recent paper it was concluded that for on-board methane storage "the preferred option is to store the gaseous fuel at high pressures, e.g. 17 MPa [2500 psig] or higher, without the use of sorbents". Indeed, it was also stated that "it is difficult to imagine on-board methane storage below about 17 MPa, unless a very good sorbent is employed". This paper entitled "Sorbent-Containing Storage Systems For Natural Gas Powered Vehicles" by Amos Golovoy, was presented at a meeting of the Society of Automotive Engineers, Detroit, Mich., February 1983, and is hereby incorporated by reference.
Accordingly, in spite of significant and extensive research and development efforts in the area of gaseous fuel powered vehicles, no natural gas fuel storage or refueling systems have emerged that apply adsorptive storage technology to on-board vehicular storage and to their refueling apparatus. In fact, the above-discussed compressed natural gas and liquefied natural gas systems have been generally regarded as the only two feasible systems for natural gas powered vehicle applications.
The need has thus arisen for a hydrocarbon gaseous fuel powered vehicle that is capable of providing reasonable quantities of on-board fuel storage at relatively low pressures, and for practical and inexpensive refueling apparatus allowing such a vehicle to be refueled by the user from a residential natural gas supply system.
One of the primary objectives of the present invention is to provide a low pressure gaseous hydrocarbon fuel storage system and power plant for a vehicle in which sorption is used to reduce the pressure at which the gaseous hydrocarbon fuel is stored.
Another objective of the present invention is to provide a low pressure gaseous hydrocarbon fuel stored system and power plant in which the gaseous hydrocarbon fuel is sorptively filtered before being conveyed to a storage means on-board the vehicle. A related objective is to provide an sorptive filter which is self-cleaning during the operation of the vehicle.
A further objective of the present invention is to provide a low pressure gaseous hydrocarbon fuel storage system and power plant which is capable of utilizing a plurality of storage vessels in order to provide a self-contained supply of the gaseous hydrocarbon fuel on board the vehicle.
An additional objective of the present invention is to provide a low pressure gaseous hydrocarbon fuel storage system and power plant which is capable of being utilized in both single fuel and dual fuel supply systems.
It is yet another objective of the present invention to provide a low pressure gaseous hydrocarbon fuel storage system and power plant which is capable of being charged from either a high pressure or low pressure stationary source of the gaseous hydrocarbon fuel.
It is a more specific objective of the present invention to provide a vehicular natural gas storage system and power plant which is economical, operates at pressures below 500 psig, (3450 kPa) and also provides for a reasonable driving range.
To achieve the foregoing objectives, the present invention provides a low pressure gaseous hydrocarbon fuel storage system and power plant, which generally comprises means for storing a self-contained supply of the gaseous hydrocarbon fuel, a prime mover, means for conveying the gaseous hydrocarbon fuel to and from the storing means, and means for controlling the flow of the gaseous hydrocarbon fuel from the storing means to the prime mover. The storing means, which may include one or more vessels or cylinders, contains a predetermined sorbent material for reducing the pressure at which a given amount of the gaseous hydrocarbon fuel is stored. The prime mover, such as an internal combustion engine, has means for combining the gaseous hydrocarbon fuel with air to produce the mechanical energy therefrom necessary to move the vehicle. The conveying means is adapted to convey the gaseous hydrocarbon fuel to the storing means from a stationary source of the gaseous hydrocarbon fuel, and also to convey the gaseous hydrocarbon fuel from the storing means to the combining means of the prime mover during the operation of the vehicle. In the preferred embodiment, the maximum pressure at which the gaseous hydrocarbon fuel is stored in the storing means is in the range of approximately 100 psig (689 kPa) to approximately 400 psig (2760 kPa).
One of the significant advantages of the present invention is the use of a sorptive filter which is interposed in the conveying means between the storage means and the prime mover. When the vehicle fuel storage system is being charged, this filter sorptively removes predetermined constituents from the gaseous hydrocarbon fuel before the gaseous hydrocarbon fuel is conveyed to the storing means. Subsequently, when the prime mover is energized and the gaseous hydrocarbon fuel is conveyed from the storage means to the prime mover for consumption therein, the filter desorptively reintroduces the removed predetermined constituents to the flow of the gaseous hydrocarbon fuel being conveyed to the prime mover. Accordingly, the adsorptive filter not only prevents certain undesirable fuel constituents or contaminants from being introduced into the storage means, but it also operates as a self-cleaning or regenerative filter during the operation of the vehicle.
Another significant aspect of the present invention arises in connection with the use of a plurality of vessels or cylinders to store the gaseous hydrocarbon fuel. Specifically, a manifold means is provided for distributing the gaseous hydrocarbon fuel received from the stationary source to each of the plurality of vessels and for collecting the gaseous hydrocarbon fuel stored in one or a plurality of vessels in order to convey this fuel to the prime mover or engine. The manifold means also operates to equalize pressure, to insure that the pressure in the vessels do not exceed a predetermined pressure, filters the gaseous hydrocarbon fuel flow to the vessels, senses the pressure within the vessels, and is capable of selectively controling the flow of fuel to and from the storage vessels. The storage vessels may also be enclosed in one or more chambers which are separated from the passenger compartment of the vehicle, and vented to the atmosphere exterior of the vehicle.
Additional objects, advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.